Non-native species are one of the greatest threats to biodiversity worldwide due to their direct and indirect effects on native communities. There are two opposing hypotheses to explain how non-native species successfully establish outside their native range. The first posits that non-native species are closely related to local native species through environmental filtering, which selects species with similar traits; the second posits that non-native species are distantly related to native species in the area in which they establish due to limiting similarity, which minimizes competition. We assessed support for these two hypotheses by characterizing the functional trait space of terrestrial bird communities in Italian cities. We surveyed 220 points in breeding and winter periods along an urbanization gradient in six cities. We assessed whether two non-native bird species, Rose-ringed Parakeet Psittacula krameri and Monk Parakeet Myiopsitta monachus, conformed to either of the two opposing hypotheses by calculating functional diversity metrics (Functional Dispersion, i.e. quantification of the distribution of functional elements in the niche space, and Contribution, i.e. contribution of each species to the niche space) for each community. We then modelled these metrics in relation to the presence or absence of the two non-native parakeet species along the urbanization gradient. We found that non-native parakeet species probably established in the vacant functional niche space of urban bird communities. Our results support the hypothesis that limiting similarity allows the establishment of non-native parakeets at the local scale by reducing competition with native species due to trait dissimilarity. Urban environments offer novel opportunities for the parakeets that are not exploited by the native species present. This insight into niche space processes in urban areas, which can act as centres for expansion of non-native birds into other environments, can be used when implementing management strategies to enhance environmental filtering in these areas, thus reducing the chances of further establishment of non-native species.
Non‐native parrot species expand the trait space of avian communities by filling empty niches in urban areas
Mammola, Stefano;Rubolini, Diego;
2026
Abstract
Non-native species are one of the greatest threats to biodiversity worldwide due to their direct and indirect effects on native communities. There are two opposing hypotheses to explain how non-native species successfully establish outside their native range. The first posits that non-native species are closely related to local native species through environmental filtering, which selects species with similar traits; the second posits that non-native species are distantly related to native species in the area in which they establish due to limiting similarity, which minimizes competition. We assessed support for these two hypotheses by characterizing the functional trait space of terrestrial bird communities in Italian cities. We surveyed 220 points in breeding and winter periods along an urbanization gradient in six cities. We assessed whether two non-native bird species, Rose-ringed Parakeet Psittacula krameri and Monk Parakeet Myiopsitta monachus, conformed to either of the two opposing hypotheses by calculating functional diversity metrics (Functional Dispersion, i.e. quantification of the distribution of functional elements in the niche space, and Contribution, i.e. contribution of each species to the niche space) for each community. We then modelled these metrics in relation to the presence or absence of the two non-native parakeet species along the urbanization gradient. We found that non-native parakeet species probably established in the vacant functional niche space of urban bird communities. Our results support the hypothesis that limiting similarity allows the establishment of non-native parakeets at the local scale by reducing competition with native species due to trait dissimilarity. Urban environments offer novel opportunities for the parakeets that are not exploited by the native species present. This insight into niche space processes in urban areas, which can act as centres for expansion of non-native birds into other environments, can be used when implementing management strategies to enhance environmental filtering in these areas, thus reducing the chances of further establishment of non-native species.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
